Dishwasher appliances generally include a tub that defines a wash chamber. Rack assemblies can be mounted within the wash chamber of the tub for receipt of articles for washing. Wash fluid (e.g., various combinations of water and detergent along with optional additives) may be introduced into the tub where it collects in a sump space at the bottom of the wash chamber. During wash and rinse cycles, a pump may be used to circulate wash fluid to spray assemblies within the wash chamber that can apply or direct wash fluid towards articles disposed within the rack assemblies in order to clean such articles. During a drain cycle, a pump may periodically discharge soiled wash fluid that collects in the sump space and the process may be repeated.
Conventional dishwasher appliances use two separate motors to operate a wash pump and a drain pump. However, additional motors take up more space, add cost, and require additional seals, thus increasing the likelihood of leaks and decreasing appliance reliability. Certain dishwasher appliances have eliminated the need for a second motor by using a single motor and a common drive shaft to rotate a wash pump impeller and a drain pump impeller. In this regard, the wash pump impeller and the drain pump impeller may be separated by a filter, and the motor may rotate in one direction to circulate wash fluid (i.e., the “wash direction”) and the other to drain wash fluid (i.e., the “drain direction”).
However, because impellers have the tendency to pump fluid even when rotated in the reverse direction (albeit less efficiently), the drain pump impeller may discharge water from the sump even when the motor is rotating in the wash direction. Certain dishwasher appliances have attempted to prevent this issue using complicated valve systems or one-way clutches, but these solutions may be expensive and/or increase the load on the motor.
Accordingly, a dishwasher appliance that utilizes a single motor and common drive shaft to rotate a wash pump and a drain pump would be useful. More specifically, a drain pump assembly that does not pump fluid when the common drive shaft is rotated in the wash direction would be particularly beneficial.